Current seat belt systems maintain a constant, sometimes objectionable, pressure on a vehicle occupant's shoulder. This uncomfortable pressure may cause the occupant not to use the seat belt system at all or to adjust the shoulder portion of the seat belt in a manner that creates an unsafe situation. In vehicles having airbags, seat belt use is crucial to the effectiveness of the airbags. The inflatable safety devices don't work as well on unbelted passengers.
Previous systems have been designed to remove the pressure of the seat belt from the vehicle occupant in order to promote comfort and thereby the greater use of seat belts. One known seat belt system is the "window-shade" type whereby the seat belt locks in a position away from the body when it is slowly extended. A drawback to such a system is the resulting distance between the seat belt and the occupant, a distance which is fully controllable by the seat belt user and which is often excessive.
The known prior art also discloses automatic seat belt adjustment systems that include belt rewinding mechanisms which release a portion of the seat belt from a position snug against an occupant to provide tensionless comfort to the occupant. One such known system is disclosed in U.S. Pat. No. 4,655,312 issued to Frantom et al. The Frantom et al. reference discloses a seat belt system which upon sensing the seat belt being buckled, a signal is generated which activates a power control to energize the retractor's motor to snug up the seat belt against the occupant's shoulder. A logic control senses when the seat belt is snugged up with a predetermined force and terminates retraction of the seat belt. The logic control then activates a motor power control to reverse the direction of the retractor's motor to play out a small predetermined length of the seat belt. This action relaxes the shoulder portion of the seat belt, thereby removing pressure exerted on the occupant's shoulder and resulting in the occupant feeling unencumbered by the seat belt system. Frantom et al., however, discloses a system that requires extensive modifications to an existing seat belt system. Frantom et al. also discloses a seat belt system that releases the seat belt from the reel rather than from the shoulder portion of the seat belt which does not translate into any significant looseness of the belt.